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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Thermokarst rates intensify due to climate change and forest fragmentation in an Alaskan boreal forest lowland

Abstract Lowland boreal forest ecosystems in Alaska are dominated by wetlands comprised of a complex mosaic of fens, collapse‐scar bogs, low shrub/scrub, and forests growing on elevated ice‐rich permafrost soils. Thermokarst has affected the lowlands of the Tanana Flats in central Alaska for centuries, as thawing permafrost collapses forests that transition to wetlands. Located within the discontinuous permafrost zone, this region has significantly warmed over the past half‐century, and much of these carbon‐rich permafrost soils are now within ~0.5 °C of thawing. Increased permafrost thaw in lowland boreal forests in response to warming may have consequences for the climate system. This study evaluates the trajectories and potential drivers of 60 years of forest change in a landscape subjected to permafrost thaw in unburned dominant forest types (paper birch and black spruce) associated with location on elevated permafrost plateau and across multiple time periods (1949, 1978, 1986, 1998, and 2009) using historical and contemporary aerial and satellite images for change detection. We developed (i) a deterministic statistical model to evaluate the potential climatic controls on forest change using gradient boosting and regression tree analysis, and (ii) a 30 × 30 m land cover map of the Tanana Flats to estimate the potential landscape‐level losses of forest area due to thermokarst from 1949 to 2009. Over the 60‐year period, we observed a nonlinear loss of birch forests and a relatively continuous gain of spruce forest associated with thermokarst and forest succession, while gradient boosting/regression tree models identify precipitation and forest fragmentation as the primary factors controlling birch and spruce forest change, respectively. Between 1950 and 2009, landscape‐level analysis estimates a transition of ~15 km² or ~7% of birch forests to wetlands, where the greatest change followed warm periods. This work highlights that the vulnerability and resilience of lowland ice‐rich permafrost ecosystems to climate changes depend on forest type.

Lara, Mark J.↗
NASA NTRS1996

An Automated Mapping Processor using C-Band Interferometric SAR Data

We describe a processor which has been implemented to generate map products starting from C-band interferometric data. The first stage of the processor consists of the conventional interferometric synthetic aperture radar (SAR) processing producing a digital elevation model (DEM) and a SAR brightness image in sensor coordinates. In the second stage of processing, a land use classification map is obtained by using the DEM, brightness, and interferometric correlation layers. Auxiliary layers which include a drainage layer, a height gradient layer, a height error layer, an estimated penetration layer, and a shaded relief layer are also computed. In the final step, all UTM collocated layers are combined in a geographical information system (GIS) which allows for both hard copy map products and digital applications.

Rodriguez, E.↗
NASA NTRS1996

An Automated Mapping Processor Using C-Band Interferometric SAR Data

We present the description of a processor which has been implemented to generate map products starting from C-band interferometric data. The first stage of the processor consists of the conventional interferometric SAR processing producing a Digital Elevation Model (DEMs) and a SAR brightness image in sensor coordinates. In the second stage of processing, a land use classification map is obtained by using the DEM, brightness, and interferometric correlation layers. Auxiliary layers which include a drainage layer, a height gradient layer, a height error layer, an estimated penetration layer, and a shaded relief layer are also computed. In the final step, all UTM collocated layers are combined in a GIS system which allows for both hard copy map products and for digital applications.

Rodriguez, E.↗
NASA NTRS2003

Hot Films on Ceramic Substrates for Measuring Skin Friction

Hot-film sensors, consisting of a metallic film on an electrically nonconductive substrate, have been used to measure skin friction as far back as 1931. A hot film is maintained at an elevated temperature relative to the local flow by passing an electrical current through it. The power required to maintain the specified temperature depends on the rate at which heat is transferred to the flow. The heat transfer rate correlates to the velocity gradient at the surface, and hence, with skin friction. The hot-film skin friction measurement method is most thoroughly developed for steady-state conditions, but additional issues arise under transient conditions. Fabricating hot-film substrates using low-thermal-conductivity ceramics can offer advantages over traditional quartz or polyester-film substrates. First, a low conductivity substrate increases the fraction of heat convected away by the fluid, thus increasing sensitivity to changes in flow conditions. Furthermore, the two-part, composite nature of the substrate allows the installation of thermocouple junctions just below the hot film, which can provide an estimate of the conduction heat loss.

Noffz, Greg↗
DOE OSTI2016

Structure and dynamics of aqueous solutions from PBE-based first-principles molecular dynamics simulations

Establishing an accurate and predictive computational framework for the description of complex aqueous solutions is an ongoing challenge for density functional theory based first-principles molecular dynamics (FPMD) simulations. In this context, important advances have been made in recent years, including the development of sophisticated exchange-correlation functionals. On the other hand, simulations based on simple generalized gradient approximation (GGA) functionals remain an active field, particularly in the study of complex aqueous solutions due to a good balance between the accuracy, computational expense, and the applicability to a wide range of systems. In such simulations we often perform them at elevated temperatures to artificially “correct” for GGA inaccuracies in the description of liquid water; however, a detailed understanding of how the choice of temperature affects the structure and dynamics of other components, such as solvated ions, is largely unknown. In order to address this question, we carried out a series of FPMD simulations at temperatures ranging from 300 to 460 K for liquid water and three representative aqueous solutions containing solvated Na + , K + , and Cl - ions. We show that simulations at 390–400 K with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional yield water structure and dynamics in good agreement with experiments at ambient conditions. Simultaneously, this computational setup provides ion solvation structures and ion effects on water dynamics consistent with experiments. These results suggest that an elevated temperature around 390–400 K with the PBE functional can be used for the description of structural and dynamical properties of liquid water and complex solutions with solvated ions at ambient conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Microbial Biomarker Transition in High-Altitude Sinter Mounds From El Tatio (Chile) Through Different Stages of Hydrothermal Activity

Geothermal springs support microbial communities at elevated temperatures in an ecosystem with high preservation potential that makes them interesting analogs for early evolution of the biogeosphere. The El Tatio geysers field in the Atacama Desert has astrobiological relevance due to the unique occurrence of geothermal features with steep hydrothermal gradients in an otherwise high altitude, hyper-arid environment. We present here results of our multidisciplinary field and molecular study of biogeochemical evidence for habitability and preservation in silica sinter at El Tatio. We sampled three morphologically similar geyser mounds characterized by differences in water activity (i.e., episodic liquid water, steam, and inactive geyser lacking hydrothermal activity). Multiple approaches were employed to determine (past and present) biological signatures and dominant metabolism. Lipid biomarkers indicated relative abundance of thermophiles (dicarboxylic acids) and sulfate reducing bacteria (branched carboxylic acids) in the sinter collected from the liquid water mound; photosynthetic microorganisms such as cyanobacteria (alkanes and isoprenoids) in the steam sinter mound; and archaea (squalane and crocetane) as well as purple sulfur bacteria (cyclopropyl acids) in the dry sinter from the inactive geyser. The three sinter structures preserved biosignatures representative of primary (thermophilic) and secondary (including endoliths and environmental contaminants) microbial communities. Sequencing of environmental 16S rRNA genes and immuno-assays generally corroborated the lipid-based microbial identification. The multiplex immunoassays and the compound-specific isotopic analysis of carboxylic acids, alkanols, and alkanes indicated that the principal microbial pathway for carbon fixation in the three sinter mounds was through the Calvin cycle, with a relative larger contribution of the reductive acetyl-CoA pathway in the dry system. Other inferred metabolic traits varied from the liquid mound (iron and sulfur chemistry), to the steam mound (nitrogen cycle), to the dry mound (perchlorate reduction). The combined results revealed different stages of colonization that reflect differences in the lifetime of the mounds, where primary communities dominated the biosignatures preserved in sinters from the still active geysers (liquid and steam mounds), in contrast to the surviving metabolisms and microbial communities at the end of lifetime of the inactive geothermal mound.

Lipid biomarkers, geothermal springs, sinter, biog↗
DOE OSTI2023

Uniform momentum and temperature zones in unstably stratified turbulent flows

Wall-bounded turbulent flows exhibit a zonal arrangement, in which streamwise velocity organizes into uniform momentum zones (UMZs), separated by thin layers of elevated interfacial shear. While significant research efforts have focused on these structural features in neutrally stratified flows, the effects of unstable thermal stratification on UMZs and on analogous uniform temperature zones (UTZs) have not been considered previously. In this article, statistical properties of UMZs and UTZs are investigated using a suite of large eddy simulations of unstably stratified turbulent channel flow spanning weakly to highly convective conditions. When normalized by the friction velocity and stability-dependent mixing length, the mean velocity gradient based on UMZ interfacial velocity jumps and the vorticity thickness exhibits good collapse for all stabilities, establishing a link between UMZ properties and scaling predictions from Monin–Obukhov similarity theory. A similar relationship is found between UTZ properties and surface-layer scaling of the mean temperature gradient. In the mixed layer, mean UMZ depth is quasi-constant with wall-normal distance, while the deepest UTZs are found in the centre of the boundary layer. These instantaneous structures are found to be linked to the well-mixed velocity and temperature profiles in the convective mixed layer. Conditional averaging indicates that both UMZ and UTZ interfaces are associated with ejections of momentum and warm updrafts below the interface and sweeps of momentum and cool downdrafts above the interface. These results demonstrate a tangible connection between instantaneous structural features, mean properties and scaling laws in unstably stratified flows.

Mechanics↗
DOE OSTI2014

Electric field induced transformation of carbon nanotube to graphene nanoribbons using Nafion as a solid polymer electrolyte

We report a remarkable transformation of multiwalled carbon nanotubes (MWCNTs, average diameter 40 nm) to graphene nanoribbons (GNRs) in response to a field gradient of ∼25 V/cm, in a sandwich configuration using a solid state proton conducting polymer electrolyte like a thin perfluorosulphonated membrane, Nafion. In response to the application of a constant voltage for a sustained period of about 24 h at both room temperature and elevated temperatures, an interesting transformation of MWCNTs to GNRs has been observed with reasonable yield. GNRs prepared by this way are believed to be better for energy storage applications due to their enhanced surface area with more active smooth edge planes. Moreover, possible morphological changes in CNTs under electric field can impact on the performance and long term stability of devices that use CNTs in their electronic circuitry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Seawater exposure causes hydraulic damage in dying Sitka-spruce trees

Sea-level rise is one of the most critical challenges facing coastal ecosystems under climate change. Observations of elevated tree mortality in global coastal forests are increasing, but the mechanism of salinity-stress induced tree mortality is currently unknown. We monitored progressive mortality and associated gas exchange and hydraulic shifts in Sitka-spruce (Picea sitchensis) trees located within a salinity gradient under an ecosystem-scale change of seawater exposure in Washington State, USA. Percentage of live foliated crown (PLFC) decreased and tree mortality increased with increasing soil salinity during the study period. A strong reduction in gas exchange and xylem hydraulic conductivity (Ks) occurred during tree death, with an increase of the percentage loss of xylem conductivity (PLC) and turgor loss point (ptlp). Hydraulic and osmotic shifts reflected that hydraulic function declined from seawater exposure and dying trees were unable to support osmotic adjustment. Constrained gas exchange was strongly related to hydraulic damage at both stem and leaf levels. Significant correlations between foliar sodium (Na+) concentration and gas exchange and key hydraulic parameters (Ks, PLC and ptlp ) suggest that cellular injury related to the toxic effects of ion accumulation impacted the physiology of these dying trees. This study provides evidence of toxic effects on cellular function that become manifest in all aspects of plant functioning, leading to unfavourable osmotic and hydraulic conditions.

Zhang, Hongxia↗
NASA NTRS2026

Remote Sensing-Driven Hydrodynamic Modeling in Data-Scarce Regions: Integrating ICESat-2, Sentinel-2, SWOT and Re-analysis Models for Coastal Monitoring

Hydrodynamic models in coastal and estuarine systems are typically constrained by sparse bathymetry, boundary, and validation data, especially in regions where field campaigns are costly or impractical. Here we develop and test a fully satellite-driven framework for hydrodynamic modeling in South Africa’s Langebaan Lagoon without using any local in situ measurements. Bathymetry is derived by training multispectral Sentinel-2 reflectance against ICESat-2 ATL24 photon-derived depths using an XGBoost model optimized with Bayesian search. The final satellite-derived bathymetry reproduces independent ATL24 points with RMSE = 0.45 m and R 2 = 0.97. This bathymetry was used in a depth-averaged Delft3D Flexible Mesh model driven at the open boundary by TPXO tidal harmonics and by ERA5 winds. We validate modeled water surface elevation against 16 SWOT low-rate (250 m, unsmoothed) passes in 2023. SWOT–model comparisons yield an overall RMSE of 0.11 m and R 2 = 0.61, with typical point differences <0.10 m (∼7% of the 1.5 m tidal range), and showed consistent spatial gradients in water level from the offshore boundary, through Saldanha Bay, and into the lagoon. At the offshore boundary, TPXO and SWOT sea surface heights agree closely (R 2 = 0.86). A simple phase adjustment of ∼26,min between TPXO and SWOT lowers the RMSE from 0.18,m to 0.11,m, showing that phase offset accounts for some of the discrepancy, with additional errors likely linked to non-tidal signals. Our results demonstrate that combining passive optical, photon-counting LiDAR, radar interferometry, and global tidal/atmospheric models enables robust, transferrable hydrodynamic modeling in data-scarce coastal systems, offering a cost-effective pathway for monitoring.

ICESat-2↗
DOE OSTI2021

Interpretation of electromagnetic modes in the sub-TAE frequency range in JET plasmas with elevated monotonic q-profiles

Recent JET deuterium experiments with an advanced tokamak scenario using an internal transport barrier (ITB) have been performed to clearly observe destabilized toroidicity-induced Alfvén eigenmodes (TAEs) by fast ions; interestingly, these also exhibit unstable electromagnetic (EM) perturbations in the sub-TAE frequency range. We identify such EM perturbations to be beta-induced ion temperature gradient (BTG) eigenmodes and not beta-induced Alfvén eigenmodes nor beta-induced Alfvén acoustic eigenmodes, which are often unstable in such high-beta plasmas with high-power neutral beam injection (NBI). The BTG modes are the most unstable modes due to the high thermal ion temperature gradient related to the ITB, high thermal ion temperature compared to thermal electron temperature (high T i /T⁠ e ), and a high ion beta regime. BTG mode experimental characteristics match the analytical theory, i.e., location in the vicinity of a rational magnetic surface with a low magnetic shear, mode frequency scaling with the ion diamagnetic frequency (⁠ω$^*_i$⁠), and a coupling among Alfvén and drift waves. We also perform linear gyrokinetic simulations with validated plasma profiles and equilibrium, and find a mode kinetically driven by thermal ions with similar characteristics as the experimental BTG modes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Stochastic and Deterministic Assembly Processes in Subsurface Microbial Communities

A major goal of microbial community ecology is to understand the forces that structure community composition. Deterministic selection by specific environmental factors is sometimes important, but in other cases stochastic or ecologically neutral processes dominate. Lacking is a unified conceptual framework aiming to understand why deterministic processes dominate in some contexts but not others. Here we work towards such a framework. By testing predictions derived from general ecological theory we aim to uncover factors that govern the relative influences of deterministic and stochastic processes. We couple spatiotemporal data on subsurface microbial communities and environmental parameters with metrics and null models of within and between community phylogenetic composition. Testing for phylogenetic signal in organismal niches showed that more closely related taxa have more similar habitat associations. Community phylogenetic analyses further showed that ecologically similar taxa coexist to a greater degree than expected by chance. Environmental filtering thus deterministically governs subsurface microbial community composition. More importantly, the influence of deterministic environmental filtering relative to stochastic factors was maximized at both ends of an environmental variation gradient. A stronger role of stochastic factors was, however, supported through analyses of phylogenetic temporal turnover. While phylogenetic turnover was on average faster than expected, most pairwise comparisons were not themselves significantly non-random. The relative influence of deterministic environmental filtering over community dynamics was elevated, however, in the most temporally and spatially variable environments. Our results point to general rules governing the relative influences of stochastic and deterministic processes across micro- and macro-organisms.

community assembly↗
DOE OSTI2019

Climatic controls of decomposition drive the global biogeography of forest-tree symbioses

The identity of the dominant microbial symbionts in a forest determines the ability of trees to access limiting nutrients from atmospheric or soil pools, sequester carbon and withstand the impacts of climate change. Characterizing the global distribution of symbioses, and identifying the factors that control it, are thus integral to understanding present and future forest ecosystem functioning. In this work we generate the first spatially explicit global map of forest symbiotic status using a database of over 1.1 million forest inventory plots with over 28,000 tree species. Our analyses indicate that climatic variables, and in particular climatically-controlled variation in decomposition rate, are the primary drivers of the global distribution of major symbioses. We estimate that ectomycorrhizal (EM) trees, which represent only 2% of all plant species, constitute approximately 60% of tree stems on Earth. EM symbiosis dominates forests where seasonally cold and dry climates inhibit decomposition, and are the predominant symbiosis at high latitudes and elevation. On the other hand, arbuscular mycorrhizal (AM) trees dominate aseasonally warm tropical forests and occur with EM trees in temperate biomes where seasonally warm-and-wet climates enhance decomposition. Continental transitions between AM and EM dominated forests occur relatively abruptly along climate driven decomposition gradients, which is likely caused by positive plant-microbe feedbacks. Symbiotic N-fixers, which are insensitive to climatic controls on decomposition compared with mycorrhizal fungi, are most abundant in arid biomes with alkaline soils and high maximum temperatures. The climatically driven global symbiosis gradient we document represents the first spatially-explicit, quantitative understanding of microbial symbioses at the global scale and demonstrates the critical role of microbial mutualisms in shaping the distribution of plant species.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1989

Morphology of calcite crystals in clast coatings from four soils in the Mojave desert region

Pedogenic calcite-crystal coatings on clasts were examined in four soils along an altitudinal gradient on Kyle Canyon alluvium in southern Nevada. Clast coatings were studied rather than matrix carbonate to avoid the effects of soil matrix on crystallization. Six crystal sizes and shapes were recognized and distinguished. Equant micrite was the dominant crystal form with similar abundance at all elevations. The distributions of five categories of spar and microspar appear to be influenced by altitudinally induced changes in effective moisture. In the drier, lower elevation soils, crystals were equant or parallel prismatic with irregular, interlocking boundaries while in the more moist, higher elevation soils they were randomly oriented, euhedral, prismatic, and fibrous. There was little support for the supposition that Mg(+2) substitution or increased (Mg + Ca)/HCO3 ratios in the precipitating solution produced crystal elongation.

Chadwick, Oliver A.↗
NASA NTRS1989

Shear-induced inflation of coronal magnetic fields

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z)squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

Klimchuk, James A.↗
NASA NTRS1990

Shear-induced inflation of coronal magnetic fields

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z) squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

Klimchuk, James A.↗
NASA NTRS1989

Elevated temperature crack growth

Alloy 718 crack growth experiments were conducted to assess the ability of the selected path-independent (P-I) integrals to describe the elevated temperature crack growth behavior. These tests were performed on single edge notch (SEN) specimens under displacement control with multiple extensometers to monitor the specimen and crack mouth opening displacement (CMOD). The displacements in these tests were sufficiently high to induce bulk cyclic inelastic deformation of the specimen. Under these conditions, the linear elastic fracture mechanics (LEFM) parameter K does not correlate the crack growth data. The experimentally measured displacement gradients at the end of specimen gage length were used as the boundary conditions in elastic-plastic finite element method (FEM) analyses. These analyses were performed with a node release approach using CYANIDE, a GEAE FEM code, which included a gap element which is capable of efficiently simulating crack closure. Excellent correlation was obtained between the experimentally measured and predicted variation of stress and CMOD with crack length and the stress-CMOD loops for Alloy 718 tests conducted at 538 C. This confirmed the accuracy of the FEM crack growth simulation approach. The experimentally measured crack growth rate data correlated well the selected P-I integrals. These investigations have produced significant progress in developing P-I integrals as non-linear fracture mechanics parameters. The results suggest that this methodology has the potential of accurately describing elevated temperature crack growth behavior under the combined influence of thermal cycling and bulk elastic-inelastic deformation states.

Kim, K. S.↗